/*-------------------------------------------------------------------------
 *
 * arrayaccess.h
 *      Declarations for element-by-element access to Postgres arrays.
 *
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/utils/arrayaccess.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef ARRAYACCESS_H
#define ARRAYACCESS_H

#include "access/tupmacs.h"
#include "utils/array.h"


/*
 * Functions for iterating through elements of a flat or expanded array.
 * These require a state struct "array_iter iter".
 *
 * Use "array_iter_setup(&iter, arrayptr);" to prepare to iterate, and
 * "datumvar = array_iter_next(&iter, &isnullvar, index, ...);" to fetch
 * the next element into datumvar/isnullvar.
 * "index" must be the zero-origin element number; we make caller provide
 * this since caller is generally counting the elements anyway.  Despite
 * that, these functions can only fetch elements sequentially.
 */

typedef struct array_iter
{
    /* datumptr being NULL or not tells if we have flat or expanded array */

    /* Fields used when we have an expanded array */
    Datum       *datumptr;        /* Pointer to Datum array */
    bool       *isnullptr;        /* Pointer to isnull array */

    /* Fields used when we have a flat array */
    char       *dataptr;        /* Current spot in the data area */
    bits8       *bitmapptr;        /* Current byte of the nulls bitmap, or NULL */
    int            bitmask;        /* mask for current bit in nulls bitmap */
} array_iter;


static inline void
array_iter_setup(array_iter *it, AnyArrayType *a)
{
    if (VARATT_IS_EXPANDED_HEADER(a))
    {
        if (a->xpn.dvalues)
        {
            it->datumptr = a->xpn.dvalues;
            it->isnullptr = a->xpn.dnulls;
            /* we must fill all fields to prevent compiler warnings */
            it->dataptr = NULL;
            it->bitmapptr = NULL;
        }
        else
        {
            /* Work with flat array embedded in the expanded datum */
            it->datumptr = NULL;
            it->isnullptr = NULL;
            it->dataptr = ARR_DATA_PTR(a->xpn.fvalue);
            it->bitmapptr = ARR_NULLBITMAP(a->xpn.fvalue);
        }
    }
    else
    {
        it->datumptr = NULL;
        it->isnullptr = NULL;
        it->dataptr = ARR_DATA_PTR(&a->flt);
        it->bitmapptr = ARR_NULLBITMAP(&a->flt);
    }
    it->bitmask = 1;
}

static inline Datum
array_iter_next(array_iter *it, bool *isnull, int i,
                int elmlen, bool elmbyval, char elmalign)
{
    Datum        ret;

    if (it->datumptr)
    {
        ret = it->datumptr[i];
        *isnull = it->isnullptr ? it->isnullptr[i] : false;
    }
    else
    {
        if (it->bitmapptr && (*(it->bitmapptr) & it->bitmask) == 0)
        {
            *isnull = true;
            ret = (Datum) 0;
        }
        else
        {
            *isnull = false;
            ret = fetch_att(it->dataptr, elmbyval, elmlen);
            it->dataptr = att_addlength_pointer(it->dataptr, elmlen,
                                                it->dataptr);
            it->dataptr = (char *) att_align_nominal(it->dataptr, elmalign);
        }
        it->bitmask <<= 1;
        if (it->bitmask == 0x100)
        {
            if (it->bitmapptr)
                it->bitmapptr++;
            it->bitmask = 1;
        }
    }

    return ret;
}

#endif                            /* ARRAYACCESS_H */
